1. Field of the Invention
The invention relates to a plug comprising: a body portion, an elongated conductive connector projecting from the body portion for receiving one or more conductors, at one end of which connector are arranged means for bringing said conductor into contact with a connector in a plug counterpart, a tubular capacitor threaded around the connector so as to couple an inner surface forming a first pole of the tubular capacitor to the connector, and grounding means coupled to an outer surface forming a second pole of the tubular capacitor, the grounding means being arranged to ground said second pole of the tubular capacitor.
2. Description of the Related Art
The term "elongated connector" as used herein refers to e.g. a needle-shaped fairly long connector whose length is sufficient for a tubular capacitor to be threaded thereon.
This invention relates to a disturbance shielded plug adapted for use in environments with a relatively strong interfering electromagnetic field. The plug according to the invention is adapted for use with e.g. telecommunications equipment, radio transmitters and the like. If a conventional non-shielded plug, to which e.g. a conventional multipolar cable is connected, were used in the strong RF field surrounding radio transmitters, the field surrounding the plug and the cable would cause such strong interference that hardly any useful signal could be transmitted via the cable and the plug.
It is known to utilize a conventional non-shielded plug with a shielded cable in places with a strong interfering electromagnetic field. In this case a multipolar cable is commonly used, with e.g. an aluminium foil layer arranged under an insulating material layer forming the external armature of the cable. For practical reasons a shielded cable cannot, however, be used in all places, and its cost is also relatively high compared with conventional cables.
Additionally, it is known to utilize a shielded so-called D-plug with a conventional non-shielded cable in places with a strong interfering electromagnetic field. In this case tubular capacitors are arranged around the elongated connectors in the plug. In this solution a first pole of the tubular capacitors, formed by their inner surfaces, is soldered to the connector around which that particular tubular capacitor is arranged. Furthermore, the outer surface forming a second pole of the tubular capacitors is soldered to a grounding plate in the plug. When the tubular capacitors are correctly designed, they can be used to filter e.g. interference caused by an external RF field, thus allowing the utilization of a non-shielded cable with said plug.
The most significant disadvantage of the above known shielded plug is that it is complicated to assemble. This is because each tubular capacitor must be separately soldered both to that particular connector around which it is arranged and to the grounding plate in the plug. As a plug may comprise several connectors, e.g. 64, this would result in the number of necessary solders being 128. Owing to the small size of the tubular capacitors (diameter e.g. approx. 1 to 2 mm, and height e.g. approx. 2 mm) and the lack of space in the plug, providing soldering to the right places requires extreme accuracy. Thus, the assembly of the plug is slow and expensive.